Make sure gfortran is available during Azure CI

azure-pipelines.yml

@@ -31,6 +31,8 @@ jobs:
         script: |
             set -e
             CONDA_ENVIRONMENT=.test-conda-env-py3.yml
+            sudo apt install gfortran-7
+            sudo ln -s /usr/bin/gfortran-7 /usr/bin/gfortran
             curl -L -O -k https://gitlab.tiker.net/inducer/ci-support/raw/master/build-and-test-py-project-within-miniconda.sh
             . ./build-and-test-py-project-within-miniconda.sh